The robust, sensitive, and selective detection of targeted biomolecules in their native environment by prospective nanostructures holds much promise for real-time, accurate, and high throughput biosensing. However, in order to be competitive, current biosensor nanotechnologies need significant improvements, especially in specificity, integration, throughput rate, and long-term stability in complex bioenvironments. Advancing biosensing nanotechnologies in chemically "noisy" bioenvironments require careful engineering of nanoscale components that are highly sensitive, biorecognition ligands that are capable of exquisite selective binding, and seamless integration at a level current devices have yet to achieve. This review summarizes recent advances in the synthesis, assembly, and applications of nanoengineered reporting and transducing components critical for efficient biosensing. First, major classes of nanostructured components, both inorganic reporters and organic transducers, are discussed in the context of the synthetic control of their individual compositions, shapes, and properties. Second, the design of surface functionalities and transducing path, the characterization of interfacial architectures, and the integration of multiple nanoscale components into multifunctional ordered nanostructures are extensively examined. Third, examples of current biosensing structures created from hybrid nanomaterials are reviewed, with a distinct emphasis on the need to tailor nanosensor designs to specific operating environments. Finally, we offer a perspective on the future developments of nanohybrid materials and future nanosensors, outline possible directions to be pursued that may yield breakthrough results, and envision the exciting potential of high-performance nanomaterials that will cause disruptive improvements in the field of biosensing.
A unique case of combined enhanced mechanical performance and tunable structural color for chiral composites from cellulose nanocrystals (CNCs) arises by adding nanofibrillar wood-derived polymers with similar chemical compositions. When amorphous polysaccharides (pullulan, dextran, and xylan) are added, they intercalate seamlessly into the original helicoidal organization via interstitial volumes within nanocrystals and between nematic monolayers. The polysaccharides fill the available free volume in between packed nanocrystals until 40 wt% content is reached, with no phase separation occurring. Due to the inter-nanocrystal intercalation, these natural polysaccharide-cellulose composites show a nearly twofold increase in toughness and modulus. Beyond improved mechanics, the preserved iridescence shows a dramatic red shift from blue to near-infrared region, expanding the initial pitch length without disturbing the long-range chiral ordering. In the mechanistic model suggested here, the individual backbones first form intercalated morphologies in the interstitial volumes between tightly packed nanocrystals. After this, the polysaccharides form a monolayer, and eventually double layer, between nanocrystal monolayers, thus incrementally "unwinding" initial chiral organization. The resulting CNC-polysaccharide films maintain their vivid iridescence with broad color appearance and are among the first entirely biobased composites to maintain iridescence with improved mechanics.
The recent interest in reconfigurable soft materials may lead to the next paradigm in the development of adaptive and actuating materials and structures. Actuating soft materials eventually can be precisely designed to show stimuli-sensing, multi-length scale actuation, tunable transport, programmed shape control and multifunctional orthogonal responses. Herein, we discuss the various advances in the emerging field of reconfigurable soft materials with a focus on the various parameters that can be modulated to control a complex system behavior. In particular, we detail approaches that use either long-range fields (i.e. electrical, magnetic) or changes in local thermodynamic parameters (e.g., solvent quality) in order to elicit a precise dimensional and controlled response. The theoretical underpinnings and practical considerations for different approaches are briefly presented alongside several illustrative examples from the recent studies. In the end, we summarize recent accomplishments, critical issues to consider, and give perspectives on the developments of this exciting research field.
We showed large area uniformly aligned chiral photonic bioderived films from a liquid crystal phase formed by a cellulose nanocrystal (CNC) suspension placed in a thin capillary. As a result of the spatial confinement of the drying process, the interface between coexisting isotropic and chiral phases aligns perpendicular to the long axis of the capillary. This orientation facilitates a fast homogeneous growth of chiral pseudolayers parallel to the interface. Overall, the formation of organized solids takes hours vs weeks in contrast to the slow and heterogeneous process of drying from the traditional dish-cast approach. The saturation of water vapor in one end of the capillary causes anisotropic drying and promotes unidirectional propagation of the anisotropic phase in large regions that results in chiral CNC solid films with a uniformly oriented layered morphology. Corresponding ordering processes were monitored in situ at a nanoscale, mesoscale, and microscopic scale with complementary scattering and microscopic techniques. The resulting films show high orientation order at a multilength scale over large regions and preserved chiral handedness causing a narrower optical reflectance band and uniform birefringence over macroscopic regions in contrast to traditional dish-cast CNC films and those assembled in a magnetic field and on porous substrates. These thin films with a controllable and well-identified uniform morphology, structural colors, and handedness open up interesting possibilities for broad applications in bioderived photonic nanomaterials.
A simple and widely applicable approach to assemble long-range two-dimensional mobile arrays of functionalized nickel nanorods with tunable and "highly open" lattice structures is presented. The magnetic assembly of uniformly oriented nanorods in triangular lattices was achieved by a phase separation of the surface confined yet mobile vertical nanorods driven by a gradient magnetic field. In contrast to known approaches, the unfrustrated lattices can be further locked in place allowing for the removal of the applied magnetic field and processing without disrupting the initial order with different symmetries precisely assembled and locked in their position on the same substrate. We suggest that the tunable assemblies of magnetic nanorods provide a versatile platform for downstream handling of open lattice arrays for eventual device integration.
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